Unit 1 Communication, Homeostasis and Energy

     What is aerobic respiration?

What is anaerobic respiration?

Which organelle carries out most of the stages of respiration in eukaryotic cells?

What are the products of aerobic respiration?

What is the universal energy currency molecule?

 Outline why plants, animals and microorganisms need to respire, with reference to active transport and metabolic reactions.

    In order to maintain life, organisms need a source of energy. In most organisms this is provided by the oxidation of organic molecules.

Autotrophic nutrition  Synthesise organic materials from inorganic sources e.g. photosynthesis Heterotrophic nutrition  Obtained in organic form

  Energy is the ability to do work Energy exists in two states   Kinetic energy ▪ Energy of motion Potential energy ▪ Stored energy

 Energy facts     Cannot be created or destroyed Can be converted from one form to another Takes a variety of forms Measured in joules or kilojoules



Metabolism

   All reactions that take place within the organism

Anabolism

▪ Build up of larger, more complex molecules from smaller, simpler ones

Catabolism

▪ ▪ Breakdown of complex molecules into smaller, simpler ones Releases energy

 “Work”      Synthesis of complex substances Active transport e.g. sodium-potassium pump Movement Bioluminescence Maintenance of body temperature    Production of electricity Maintenance, repair and division Activation of chemicals

   Energy is defined as the ability to do ________________.

The energy of motion is known as ___________ energy, whereas _________ energy is stored energy.

Living organisms need energy for many reasons  __________ reactions in which simple molecules are built up into complex ones  The movement of material by __________ against a concentration gradient.

1.

2.

 Fireflies can produce light in a process called bioluminescence. Outline the energy transformations that occur in fireflies as they use energy from their food to produce luminescence.

Comment on the statement below.

Respiration produces energy to form ATP.

  Describe, with the aid of diagrams, the structure of ATP.

State that ATP provides the immediate source of energy for biological processes.

 ATP is a phosphorylated nucleotide.

  Adenosine ▪ ▪ Adenine Ribose sugar Three phosphate groups

 Covalent bonds between phosphate groups are unstable and easily broken releasing energy ▪ ▪ ▪ ATP ADP   AMP  ADP AMP = 30.6kJmol

= 30.6kJmol

-1 -1 Adenosine = 14.2kJmol

-1 (energy) (energy) (energy)

   As ATP is hydrolysed energy is immediately available to the cell in small, manageable amounts.

ATP is described as the universal energy currency.

ATP is continually being hydrolysed and resynthesised.

   What type of base is adenine?

ATP is a nucleic acid / nucleotide derivative.  Is it derived from DNA or RNA nucleotides?

 Give reasons for your answer Explain why ATP is known as the universal energy currency.

   explain the importance of coenzymes in respiration, with reference to NAD and coenzyme A; state that glycolysis takes place in the cytoplasm outline the process of glycolysis;

 

The oxidation of food to obtain free energy (ATP) Respiration of glucose can be summarised in four stages

    Glycolysis The link reaction Krebs cycle Oxidative Phosphorylation

 Oxidation   Loss of electrons Loss of hydrogen atoms  Reduction   Gain of electrons Gain hydrogen atoms

OIL RIG

 If one substrate becomes oxidised another becomes reduced.

   During respiration, hydrogen atoms are removed from substrate molecules in oxidation reactions.

This is catalyzed by dehydrogenase enzymes Co enzymes are required to activate the oxidation reactions in respiration  Hydrogen atoms becomes attached to co enzymes e.g. NAD

 Nicotinamide adenine dinucleotide (NAD   Is reduced when it has accepted two hydrogen atoms with their electrons Operates in glycolysis, link reaction, the Krebs cycle and the anaerobic pathways.

 Function   To carry ethanoate (acetate) groups made in the link reaction, onto the Krebs cycle To carry acetate groups made from fatty acids or amino acids onto the Krebs cycle

   Ancient biochemical pathway Glucose (6C) is broken down into two molecules of pyruvate (3C), with a net gain of 2 ATP molecules.

Occurs in the cytoplasm

 Pathway can be outlined in four stages     Phosphorylation Splitting of hexose 1,6-bisphosphate Oxidation of triose phosphate Conversion of triose phosphate to pyruvate

   Net gain of two ATP molecules Two molecules of reduced NAD Two molecules of pyruvate

 Enzymes that cause the shape of a molecule to change (without changing in proportions of atoms in that molecule) are called isomerases.

  At which stage of glycolysis are isomerase enzymes involved?

How does the fact the nearly all living things use the glycolysis pathway support the theory of evolution?

    recall the structure of a liver mitochondrion identify inner and outer membranes and the inter membranal space state that, during aerobic respiration in animals, pyruvate is actively transported into mitochondria; explain, with the aid of diagrams and electron micrographs, how the structure of mitochondria enables them to carry out their functions;

    All mitochondria have an inner and outer phospholipid membrane (envelope) Inner membrane is folded into cristae Intermembrane space Matrix    Contains looped DNA Mitochondrial ribosomes enzymes

  This is where the link reaction and the Krebs cycle take place It contains      Enzymes Molecules of coenzyme NAD Oxaloacetate Mitochondrial DNA Mitochondrial ribosomes

 It contains   Protein channels or carriers to allow pyruvate to pass through Other proteins act as enzymes

   Has a different membrane structure and is impermeable to small ions (e.g. hydrogen ions) Folded into cristae to give a large surface area Contains electron carriers and ATP synthase enzymes

  It has been suggested that mitochondria are derived from prokaryotes. What features of their structure support this suggestion?

Suggest how the structure of a mitochondria from a skin cell would differ from that of a mitochondrion from heart muscle tissue.

   state that the link reaction takes place in the mitochondrial matrix; outline the link reaction, with reference to decarboxylation of pyruvate to acetate and the reduction of NAD; explain that acetate is combined with coenzyme A to be carried to the next stage;

   Pyruvate is actively transported into the matrix of the mitochondria.

Pyruvate is dehydrogenated and decarboxylated to acetate in a series of enzyme controlled reactions.

Enzymes   Pyruvate dehydrogenase Pyruvate decarboxylase

   NAD accepts the hydrogen ions Coenzyme A accepts acetate to form Acetyl CoA, to carry onto the Krebs cycle.

Carbon dioxide is released

   state that the Krebs cycle takes place in the mitochondrial matrix; outline the Krebs cycle, with reference to the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs

  Takes place in the mitochondrial matrix Main stages    Decarboxylation ▪ Removal of Co 2 Dehydrogenation ▪ reduction of NAD Substrate-level phosphorylation ▪ Production of ATP

  For each original glucose molecule there are two turns of the Krebs cycle.

Products      6 reduced NAD 2 reduced FAD 4 carbon dioxide 2 ATP Although oxygen is not used up in these stages, they can not take place if it is absent – they are aerobic stages

Product per molecule of glucose Reduced NAD Reduced FAD CO 2 ATP Glycolysis Link reaction Krebs cycle

Product per molecule of glucose Reduced NAD Reduced FAD CO 2 ATP Glycolysis Link reaction Krebs cycle

2 0 0 2 2 0 2 0 6 2 4 2

 Moving into the last stage of aerobic respiration   10 reduced NAD 2 reduced FAD

 Explain why mature erythrocytes cannot carry out the link reaction or Krebs cycle

  The inner mitochondrial membranes are impermeable to reduced NAD. For this reason a shunt mechanism moves hydrogen ions from reduced NAD made during glycolysis, to the matrix side of the inner mitochondrial membrane. The hydrogens are carried in by another chemical than then becomes reoxidised, reducing NAD that is already in the mitochondrial matrix.

Explain why such a shunt mechanism is not required for NAD reduced during the link reaction and Krebs cycle.

  Aerobic prokaryotes can carry out the link reaction, Krebs cycle and oxidative phosphorylation. Suggest where in the prokaryotic cell these reactions take place.

  outline the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae; state that oxygen is the final electron acceptor in aerobic respiration;

    Formation of ATP by adding a phosphate group to ADP Takes place in the presence of oxygen Oxygen is the final electron acceptor Takes place across the inner mitochondrial membrane

   Reduced NAD and reduced FAD are reoxidised when they donate the hydrogen, split into H + and e Electrons are accepted by electron carriers Protons go into solution in the matrix

   Electrons passed along chain of carriers, energy released is used to pump protons across to intermembrane space building up a proton/ pH / electrochemical gradient Hydrogens diffuse through ion channels associated with ATPsynthase (chemiosmosis)

  As protons flow through ATP synthase  Drive the rotation of part of enzyme  This joins ADP and P i to form ATP Electrons and hydrogen ions combine with oxygen to form water.

  outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATPsynthase evaluate the experimental evidence for the theory of chemiosmosis

    The complete oxidation of one molecule of glucose produces a net yield of 32 ATP’s.

Energy required to make ATP comes from:  Respiration – energy released by rearranging chemical bonds  The transfer of electrons by electron carriers in mitochondria H + ions create a concentration gradient through a protein channel;  this protein channel acts as the enzyme ATP synthase. 3 H + ions provide the energy to make one ATP molecule, provided that ADP and Pi are available.

    Build of hydrogen ions on one side of membrane is a source of potential energy Movement of ions across the membrane down an electrochemical gradient – provides energy to form ATP from ADP and P i .

Inner mitochondrial membrane =

energy transducing membrane

Kinetic energy of the flow of ions =

proton motive force

 On the hand out – write out how each piece of evidence supports the chemiosmosis theory put forward by Mitchell in 1961.

  pH gradient across the membranes in involved in ATP production  The pH on one side of the membrane is higher than the other  This suggests hydrogen ions are being actively moved across the membrane Membranes make ATP even if there is no electron transport taking place, as long as a pH gradient is produced.

  Explain why was it important to keep the thylakoids in the dark?

Explain why the pH inside and outside the thylakoid membranes becomes equal when they are left in pH4 buffer for some time.

   Does a pH4 buffer contain a greater or smaller concentration of H + than a pH8 buffer?

In which direction was there a pH gradient when the thylakoids were place in the pH8 buffer?

Explain why and how the thylakoids were able to make ATP when they were placed in the pH8 buffer solution.

 Chemicals that prevent hydrogen ions being transported across the membrane also stop ATP being produced.

  Dinitrophenol is a chemical that acts as a hydrogen carrier across membranes.

If Dinitrophenol is added – no hydrogen ion gradient is built up.

 The hydrogen ion gradient is responsible for making ATP not the electron transport.

 explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration;

 Summary aerobic respiration    Glucose is oxidised to pyruvate in glycolysis Pyruvate is oxidised in Krebs Cycle Hydrogen ions removed are passed along the electron transport chain ▪ ▪ For every two hydrogen donated to the ETC by reduced NAD – 3 ATP molecules are made For every two hydrogen donated to the ETC by reduced FAD – 2 ATP molecules are made

 Some energy has been put in to these processes.

  For every two hydrogen donated to the ETC by reduced NAD – 2.5 ATP molecules are made For every two hydrogen donated to the ETC by reduced FAD – 1.5 ATP molecules are made

process Glycolysis Link reaction Krebs cycle

Phosphorylation of glucose Direct phosphorylation of ADP From reduced NAD From reduced NAD Direct phosphorylation of ADP From reduced NAD From reduced FAD

Totals Net yield ATP used ATP produced

Glycolysis Link reaction Krebs cycle process

Phosphorylation of glucose Direct phosphorylation of ADP From reduced NAD From reduced NAD Direct phosphorylation of ADP From reduced NAD From reduced FAD

Totals Net yield ATP used

2 2

ATP produced

4 5 5 2 15 3 34

32

    Transport ADP into mitochondria from the cytoplasm Transport ATP from mitochondria into the cytoplasm Protons could “leak” across membrane reducing the number to generate the proton motive force.

Active transport of pyruvate into mitochondria

  Read the information supplied at the top of the practical sheet.

Set up the three test tubes as shown below.

▪ ▪ ▪ 10ml glucose 10ml yeast 5 ml dye

 Shake tubes vigorously for 20 seconds, and place in a water bath set at 37 o C.

 Leave for a few minutes  Write up the experiment using the back of the sheet.

 Tube A    Colour change from blue via pink to colourless.

Hydrogen has been rapidly released and has reduced the dye.

For this to happen – dehydrogenase enzymes present in yeast cells must have acted on the glucose, the respiratory substrate, and oxidised it.

 Tube B    Change from blue – pink – colourless Reaction is slower since no glucose was added.

Dehydrogenase could only act on any small amount of respiratory substrate already present in the yeast cells.

 Tube C  Boiling has killed the yeast and denatured the dehydrogenase enzymes.

  explain why anaerobic respiration produces a much lower yield of ATP than aerobic respiration; compare and contrast anaerobic respiration in mammals and in yeast;

    Occurs when free oxygen is not available oxygen is no longer the final hydrogen acceptor Reduced NAD cannot be recycled to NAD The stages of respiration inside the mitochondrion can not take place

  Two other pathways recycle the reduced NAD formed during glycolysis  Alcoholic fermentation ▪ Conversion of pyruvate to ethanol  Lactate fermentation ▪ Conversion of pyruvate to lactate Both pathways are inefficient and provide a net gain of two ATP molecules per glucose molecule

  Pyruvate is decarboxylated to form ethanal Ethanal accepts hydrogen from reduced NAD to form ethanol  The alcoholic fermentation pathway is irreversible

 Pyruvate accepts the hydrogen and is converted into lactate   The lactate pathway is reversible by the Cori cycle in the mammalian liver Lactate causes a fall in pH which may stop the muscles from contracting.

  define the term respiratory substrate; explain the difference in relative energy values of carbohydrate, lipid and protein respiratory substrates

 Molecules from which energy can be liberated to produce ATP in a living cell.

 Below are 3 respiratory substrates and their energy value    Glucose Lipid Protein 16kJg -1 39kJg -1 17kJg -1

  Fatty acids enter the Krebs cycle after being broken down into two Acetyl CoA molecules Amino acids are deaminated  Converted either into pyruvate and enter the link reaction or acetate and enter the Krebs cycle

Protein Amino Acids Glycogen or starch Glucose Pyruvate Acetylcoenzyme A Krebs cycle Lipid fatty Acids

 The more hydrogens there are in the structure of a molecule, the greater the energy value 

Revise the structure of glucose, amino acids and fatty acids from the AS course.



The respiratory quotient (RQ) is the ratio of the volumes of oxygen absorbed and carbon dioxide given off in respiration.

RQ = Volume of carbon dioxide given off Volume of oxygen taken in

 Calculate the RQ for the aerobic respiration of Glucose.

 Calculate the RQ for the fatty acid oleic acid, when respired aerobically.

 C 18 H 34 O 2 + 25.5O

2  18 CO 2 + 17 H 2 O

C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2  A high RQ value suggests that anaerobic respiration is taking place.

 No RQ can be calculated for the lactate pathway as no carbon dioxide is given off.

 The respiratory quotients of different respiratory substrates are well documented from previous investigations.  Carbohydrate 1.0

  Protein Fat 0.9

0.7

 It is possible to deduce which substrate is being used by the metabolism at a specific time.  NB if a mixture of substrates is being used then the figure will be different from those above.

   Sodium hydroxide absorbs all CO 2 the air in the apparatus from the beginning. from As the germinating seeds use oxygen and the pressure reduces in tube A so the manometer level nearest to the seeds rises. Any CO 2 excreted is absorbed by the sodium hydroxide solution.

   The syringe is used to return the manometer fluid levels to normal. The volume of oxygen used is calculated by measuring the volume of gas needed from the syringe to return the levels to the original values If water replaces the sodium hydroxide then amount of carbon dioxide given off can be measured

  The respiratory quotient can be measured.

RQ = x + y or x - z x x where   

x

is the oxygen consumption

y

is the increase in volume of air (if more CO 2 produced than oxygen taken in) is

z

is the decrease in the volume of air (if less CO 2 produced than oxygen taken in) is